The present invention relates to luminaires having gas discharge type light sources such as fluorescent lamps and, more particularly, to an improved luminaire whose light has a spectral composition similar to natural daylight in both ultraviolet (UV) and visible light wavelength bands.
It is now recognized that natural daylight produced by the sun is a very important environmental element and that growth responses and photo-biological processes in plants, animals, and human beings are probably the result of adaptation to the intensity, periodicity and spectral composition of radiation from the sun that reaches the earth. Modern civilization has brought about drastic changes in this light environment. A major cause of this change is the widespread use of artificial light sources which grossly distort the natural balance of the various wavelengths found in sunlight energy.
Artificial light sources as fluorescent lamps used for general illumination are usually deficient in near (long wave) ultraviolet range of wavelengths (320 to 380 nanometers). Such radiation, which is found in natural daylight, is believed to be important in maintaining normal photo-biological responses. To remedy this defect fluorescent lamps of the so-called full-spectrum type have been developed utilizing, in a single envelope, a combination of phosphors which produce ultraviolet as well as visible light in approximately the same proportion as found in natural daylight. Such a lamp is disclosed, for example, in U.S. Pat. No. 3,670,193. While such full-spectrum lamps are a great improvement in providing artificial illumination closer to natural daylight, there are cost disadvantages connected with their use for some applications.
One problem connected with the use of full-spectrum fluorescent lamps arises from the fact that the phosphors used to produce the UV part of the radiation degrade more rapidly than those which produce the visible light. This requires more frequent replacement of the full-spectrum lamps than needed for conventional fluorescent lamps, and this increases operating costs.
Another problem might arise if full-spectrum lamps with optimum UV output for short periods are burned continuously as in factories and offices where employees work on the night shift. This could result in UV overexposure unless the lamps are turned off periodically. This would require substitution of other types of lighting resulting in duplication of lighting fixtures.
Accordingly, it is an object of this invention to provide an improved full-spectrum luminaire arrangement which substantially reduces lamp cost.
Another object of the invention is to provide a full-spectrum luminaire in which the UV part of the radiation can be conveniently switched off while permitting continued use of the luminaire for general illumination.
A still further object of the invention is to provide a full-spectrum luminaire in which the UV part of the radiation may be switched on and off at timed intervals correlated with the time of day to simulate the periodicity of the UV part of the radiation in natural daylight.
Further objects and advantages of the invention will become apparent as the following description proceeds.